1. Field of the Invention
The present invention relates to polyolefin composites comprising natural fibers. More particularly, the present invention relates to natural fiber-filled polyolefin composites having increased strength resulting from the inclusion of a functionalized polyolefin coupling agent having a broad molecular weight distribution and containing more than about 1 mmole of functionalized monomer per 100 grams of polymer.
2. Description of Related Art
It is known in the art to prepare composites comprising thermoplastic resinous matrix materials having dispersed therein organic reinforcing fillers, such as cellulosic or lignocellulosic fibers. It is also known in the art to improve the mechanical properties of such composites by treating such fibers with coupling agents prior to their introduction into the thermoplastic resinous matrix material. The following articles are among many that make reference to known technology:    P. Jacoby, et. al., “Wood Filled High Crystallinity Polypropylene,” Wood-Plastic Conference sponsored by Plastics Technology, Baltimore, Md., Dec. 5-6, 2000;    M. Wolcott et al., “Coupling Agent/Lubricant Interactions in Commercial Wood Plastic Formulations,” 6th International Conference on Woodfiber-Plastic Composites, Madison, Wis., May 15-16, 2001;    M. Chowdhury et al., “Effect of Maleated Polyolefin Copolymer and Lubricant in Wood-Polyolefin Composites,” 6th International Conference on Woodfiber-Plastic Composites, Madison, Wis., May 15-16, 2001;    W. Sigworth, “The Use of Functionalized Polyolefins in Environmentally Friendly Plastic Composites,” GPEC 2002, Feb. 13-14, 2002, Detroit, Mich.;    J. Wefer and W. Sigworth, “The Use of Functionalized Coupling Agents in Wood-filled Polyolefins,” Wood-Plastic Composites, A Sustainable Future Conference, May 14-16, 2002, Vienna, Austria;    R. Heath, “The Use of Additives to Enhance the Properties and Processing of Wood Polymer Composites,” Progress in Woodfibre-Plastic Composites Conference 2002, May 23-24, 2002, Toronto, Canada; and    W. Sigworth, “Additives for Wood Fiber Polyolefins: Coupling Agents, Progress in Woodfibre-Plastic Composites Conference 2002, May 23-24, 2002, Toronto, Canada.
Additionally, Kokta, B. V. et al., Polym.-Plast. Technol. Eng., 28(3):247-259 (1989) studied the mechanical properties of polypropylene with wood flour. The wood flour was pretreated with polymethylene polyphenylisocyanate and silane coupling agents before adding it to the polymer.
Raj, R. G. et al., Polym.-Plast. Technol. Eng., 29(4):339-353 (1990) filled high density polyethylene with three different cellulosic fibers that had been pretreated with a silane coupling agent/polyisocyanate to improve the adhesion between the fibers and the polymer matrix.
Matuana, L. M. et al. ANTEC 3:3313-3318 (1998) studied the effect of the surface acid-base properties of plasticized PVC and cellulosic fibers on the mechanical properties of the plastic/cellulosic composite. They modified the surface of the fibers with γ-aminopropyltriethoxysilane, dichlorodiethylsilane, phthalic anhydride, and maleated polypropylene.
U.S. Pat. No. 4,717,742 discloses resin composites reinforced with silanes grafted onto organic fillers that are said to have improved durability, even at sub-zero degrees or at high temperatures, improved physical properties and can be prepared by a process, in which the organic filler is grafted with a silane coupling agent in maleated polymer matrix.
U.S. Pat. No. 4,820,749 discloses a composite material based on a polymeric or copolymeric substance which may be a thermoplastic or thermosetting material or rubber, and an organic material which is cellulosic or starch. The cellulosic material is grafted with a silylating agent. Processes for preparing this composite are also disclosed.
U.S. Pat. No. 6,265,037 discloses an improved composite structural member comprising a complex profile structural member, made of a composite comprising a polypropylene polymer and a wood fiber. The material is said to be useful in conventional construction applications.
U.S. Pat. No. 6,300,415 discloses a polypropylene composition for the production of various molded articles which are said to be excellent in moldability, mold shrinkage factor on molding, rigidity, flexibility, impact resistance, in particular low-temperature impact resistance, transparency, gloss, stress-whitening resistance, and the balance thereof; various molded articles having the above properties; a propylene composition which is suitable for a base resin for the polypropylene composition; and a process for the production thereof. The propylene composition comprises a propylene homopolymer and a propylene-ethylene copolymer.
The disclosures of the foregoing are incorporated herein by reference in their entirety.